Nice items. As I understand it the meaning of SFP is disputed, but it relates to Fire Watching (ie. keeping a look out for, and reporting fires). You can find various theories such as 'Special Fire Patrol', 'Supplementary Fire Patrol' or 'Supplementary Fire Party'.

Nice little item, as far as I know, SFP, Supplementary Fire Parties recruited by the fire service, and Street Fire Parties recruited by the ARP.
Your helmet was made by Pressed steel co, which is by the date.

That is a very long question, with multiple answers.At first there were SFP, then from 1941 FG, fire guards,which after 1943 the FG separated from the wardens service. Wardens also had a big say in alerting people of fire, then there is the FW, fire watchers, who looked out for industrial premises.
Then you also factory fire brigades, who also I believe went to help the NFS when there were large raids.
This above is only just touching on the subject.

Nice catch!
I believe one of the chief jobs of Street Fire Parties was to look out for and extinguish falling incendiary bombs. There was always the danger that one could fall on a roof, break through the tiles and start a fire in the attic without anyone noticing.
There was a particular emphasis on St Paul's Cathedral, which Winston Churchill viewed as a symbol of British defiance. By his suggestion, or so I've read, specialist parties were assigned to walk the cathedral during air raids and watch out for incendiaries.
There was only one instance when an incendiary bomb posed a threat to the cathedral, when it struck the dome, got stuck and started to melt the lead. There was a panic, but it later fell and was subsequently doused.

I quite like these Zuckerman helmets. They're never expensive. A near-mint example can commonly be had for as little as £25. Perhaps because they're not all that desirable?

I wish you luck preserving that mask. The civilian ones are particularly tricky when it comes to perishing, as I myself have learnt to my detriment.

Regards, B.B.

''Everyday you think of living. We are born to die, but I appreciate life. We live day by day, and I always say: yesterday is history, today's reality, and tomorrow's a dream.' -- Henry Flescher, Holocaust Survivor -- March 14, 1924 - August 29, 2018